Post chlorinated polyvinyl chloride (CPVC) excels in higher heat deflection temperature (HDT) compared to polyvinyl chloride and is a starting material for thermoplastic compounds for hot water pipes, and particularly pressure pipes, waste gas pipes, ducts, storage tanks, construction materials among other uses.
CPVC, in order to perform adequately for the intended use is generally formulated with impact modifiers, and flow enhancing additives among other ingredients to arrive at a balance of properties. Each additive chosen for one particular advantage often is accompanied by a corresponding undesired effect on another property. Antagonistic relationships have been observed between the following additives and properties:
______________________________________ impact modifiers vs melt flow rate " vs heat deflection temperature " vs tensile modulus " vs dynamic thermal stability " vs weathering flow enhancers vs tensile modulus " vs low temperature brittleness " vs tensile strength " vs heat deflection temperature ______________________________________
Various attempts to overcome the observed limitations to modifications of CPVC are evident in the art. U.S. Pat. No. 3,299,182 discloses a blend of halogenated polyolefin and CPVC, in particular, chlorinated substantially linear polyethylene (CPE). The preferred CPE contains about 30% to 40% by weight chlorine, and is present at from about 2 to less than 10 parts by weight per 100 weight parts of CPVC (pbw), and preferably 5 to 8 parts. It has been observed that blends of CPE with CPVC do not meet the requirements of ASTM-D1784 under cell classification 2-3-4-4-7. The minimum requirements for meeting cell classification 2-3-4-4-7 under ASTM-D1784 for a CPVC composition are a notched izod impact strength of at least 1.5 ft.multidot.lbf per inch notch (80.1 J/m of notch), a tensile strength of at least 7,000 psi (48.25 MPa), a modulus of elasticity of at least 360,000 psi (2,481 MPa), a heat deflection temperature (HDT) under a 264 psi (1.82 MPa) load of at least 100.degree. C. Specifically, CPE alone in combination with CPVC fails to meet tensile modulus and, izod impact per ASTM-D1784, long term hydrostatic design strength per ASTM-D2846, and a desired low temperature ductility.
U.S. Pat. No. 3,453,347 discloses impact strength improved CPVC on addition of amorphous rubbery polymerized alkylene monoepoxides and CPE. The particular oxirane monomers found to produce a rubbery amorphous polymer contain at least 3 consecutive carbons, for example butene-1-oxide. CPE is present at from 5 to about 10 parts and the polyepoxide is present at from about 0.25 parts to about 2.5 parts per hundred weight parts CPVC. The inherent viscosity of the parent PVC from which the chlorinated PVC is derived has a preferred level of greater than about 0.55. The blends disclosed are powder mixed and ready for injection molding.
CPVC powder compound which is in use today is required for high output extrusion processes. Higher output pounds per hour are attained with powder compound and under certain expertly operated, larger extrusion machines, output per hour has exceeded 900 lbs./hr. This narrower processing window places a high demand on a powder extrusion compound in terms of processibility. In the short amount of residence time and under high temperature and controlled shear, a powder compound must achieve complete fusion and resist decomposition in contact with surface temperatures which could otherwise break-down CPVC in a matter of minutes, rendering the fabricated article unsalable.
A high strength blend of CPVC and a styrene-acrylonitrile (SAN) copolymer is disclosed in U.S. Pat. No. 4,647,646. The blend exhibits preferably a single homogenous phase wherein the preferred embodiment consists essentially of CPVC having between 60.5% and 64.5% chlorine and styrene-co-acrylonitrile (SAN) containing between 18% and 24% acrylonitrile. The blend exhibits improved tensile strength, however a particularly high tensile strength in the absence of improved impact resistance and in particular, an absence of low temperature ductility is not useful for hot and cold water distribution system (HCWD) components such as plumbing pipes and fittings or in drain-waste-vent systems. A combination of properties is required. Upon impact modification of this blend, a loss in HDT and modulus is predicted.
An improved melt processible CPVC composition is disclosed in U.S. Pat. No. 4,584,349 ('349) comprising a CPVC polymer having chlorine content of between about 60% and 66% in combination with polymethylmethacrylate (PMMA). The blends exhibit a substantially single phase morphology and the glass transition temperature (Tg) of the blends was higher than the Tg for the CPVC and PMMA separately. Tg for amorphous polymers is highly correlated with HDT. In some applications, achieving a HDT higher than CPVC is desirable. Higher Tg and improved melt flow are achieved in '349, however compositions with high HDT and melt flow alone are not entirely acceptable for HCWD uses without additional properties, particularly, tensile strength, modulus, impact properties and low temperature properties. Attempts to balance all of the desired properties particularly for powder extrusion processing are met with sacrifices in at least one property such as HDT or tensile strength when pursuing improvements in another property. There is considerable art and less science demonstrated both for formulating a composition and in processing that composition to develop all required properties for improved HCWD compounds.
U.S. Pat. No. 4,710,533 ('533) discloses CPVC blends comprising a combination of a flow enhancing amount of alpha-methyl styrene polymers and/or alpha-methyl styrene-co-acrylonitrile, an impact modifier of ABS or MBS, lead stabilizer(s), acrylic processing aid and lubricant(s). The blends exhibit good thermal stability, impact strength and melt viscosity, however an HDT of no higher than 91.5.degree. C. is achieved. HDT is a critical property for HCWD uses, however a minimum value of 100.degree. C. is required for cell class 2-3-4-4-7. In addition, unacceptable low temperature impact performance and tensile modulus for the compositions of '533 would be expected. Addition of impact modifier might improve somewhat the impact strength but would not correct the deficiency in HDT.
Accordingly, it would be desirable to obtain a CPVC composition which meets cell class 2-3-4-4-7 higher, and a pipe derived therefrom exhibiting a minimum 180.degree. F. (82.2.degree. C.) hydrostatic design stress of 500 psi (3.5 MPa) or higher per ASTM-D2846 and has improved low temperature ductility. Such a composition and article derived therefrom which exhibits this desired combination of properties not been heretofore disclosed and represents a long felt need in the art pertaining to HCWD components. With regard to this balance of properties it would be preferable, moreover a practical necessity, for achieving this combination in an extruded or molded article directly from a powder compound. The compound must also exhibit adequate dynamic thermal stability for use in commercial extrusion and injection molding processes.